1. Field of the Invention
The present invention relates to the field of intraocular lenses, and more particularly to an intraocular lens for mounting within the posterior chamber of the eye.
2. Description of the Prior Art
The lens of the human eye is situated behind the pupil and iris and functions to focus light entering through the cornea onto the retina at the rear of the eye. The lens is a biconvex, highly transparent structure made of ectodermal cells in concentric lamellae surrounded by a thin capsule. The lens capsule is supported at its periphery of suspensory ligaments, called zonules, that are continuous with the ciliary muscle. Contraction of this muscle relaxes the zonules, allowing the lens to become more spherical and thereby altering its focal length.
Under certain conditions, it is necessary to surgically remove a portion or all of the lens. For example, a cataract condition results when the material within the lens capsule becomes clouded, thereby obstructing the passage of light through the lens. To correct this condition, two forms of surgery are used. In intracapsular cataract extraction, the entire lens is removed intact by severing the zonules or suspensory ligaments about the entire periphery of the capsule. In extracapsular cataract extraction, an incision is made through the front wall or anterior capsule of the lens and the clouded cellular material within the capsule is removed. The transparent rear wall or posterior capsule remains in place in the eye, along with the zonules and peripheral portions of the anterior capsule known as the anterior capsule flaps.
Both of these procedures correct the blockage of light caused by the cataract condition. However, the light entering through the cornea and pupil is no longer focused by a lens. A variety of devices and techniques have been employed over the years to provide a substitute for the lens that has been removed or effectively destroyed by the intracapsular and extracapsular extractions. Many of these are well described in the prior art selection of U.S. Pat. No. 4,244,060, issued to Hoffer on Jan. 13, 1981, and this discussion is hereby incorporated by reference.
Many of the early designs for intracapsular lenses were positioned within the anterior chamber of the eye. These devices were frequently of the type known as an iris clip lens, since the lens was clipped to the iris by pairs of projections which extended on opposite sides of the iris when the lens was in place. Examples of these anterior lenses are discussed in the Hoffer patent. Additional examples include the lenses disclosed in the following U.S. Pat. Nos. 3,673,616, issued to Federov et al. on July 4, 1972; 3,996,626, issued to Richards et al. on Dec. 14, 1976; 3,996,627, issued to Deeg et al. on Dec. 14, 1976; 3,925,825, issued to Reykers on Dec. 16, 1975; and, 4,079,470, issued to Deeg et al. on Mar. 21, 1978. A related type of lens is disclosed in U.S. Pat. No. 4,014,049, issued to Richards et al. on Mar. 29, 1977, which lens is mounted in the posterior chamber but is secured to the iris.
The prior art also discloses a variety of intraocular lenses which are designed for mounting within the posterior chamber. There is disclosed in the Hoffer patent, for example, a lens which is stated to be particularly adapted for implantation in the posterior chamber after extracapsular cataract extraction. The Hoffer lens includes several lens-centering filaments which extend outwardly in a common plane from the rim of the lens body. These filaments are inserted within the cleft of the capsule to secure the lens within the eye and to center the lens behind the pupil.
The Hoffer lens also includes an annular lip which projects from the rear face of the lens body and is intended to seat against the posterior capsule. At least one opening in the annular lip is provided to permit the insertion of a discission instrument therethrough and into the space behind the lens. The Hoffer patent further notes that the lip limits the progress of vitreous humor toward the anterior chamber after a discission, and may limit lens fiber growth on the posterior capsule within the lip region.
A related intraocular lens is now shown in promotional literature of CILCO, Inc. of Huntington, W. Va. and is said to be available under the designation "HOFFER RIDGE LENS." This lens includes a body portion which has a convex front surface and a planar rear surface. An annular ridge extends rearwardly from and perpendicular to the rear surface adjacent the periphery of the lens. Instead of having several fine filaments as in the patent, the HOFFER RIDGE LENS includes only a pair of curved filaments, probably of greater thickness than those contemplated in the patent, and which extend outwardly from the lens body at diametrically opposed locations. Each filament extends nearly tangentially from the lens body and, in one version they curve in a "J" configuration, with the bottom of the "J" being positioned for seating the lens within the posterior chamber. Another version uses a "C" configuration.
In U.S. Pat. No. 4,110,848, issued to Jensen on Sept. 5, 1978, there is also disclosed an intraocular lens for implantation into the posterior chamber of the eye. The Jensen lens includes a pair of loops which extend outwardly from opposite sides of the lens body at a slight rearward angle. One of the loops includes a notch disposed between its end portion and the peripheral edge of the lens body so that a temporary securement to the iris of the eye may be accomplished.
Another posterior chamber lens is available from Intermedics Intraocular Inc. of Pasadena, Calif. under the designation "LESTER POSTERIOR CHAMBER INTRAOCULAR LENS." The LESTER INTRAOCULAR LENS includes a lower or inferior closed loop which extends from the lens body and also an upper or superior J-shaped filament extending from the lens body. The superior filament includes a positioning notch located slightly inward of the base of the "J" shaped filament and opposite the free end of the filament. The LESTER INTRAOCULAR LENS also includes a single, small positioning hole slightly inward of the top edge of the lens body.
Currently available are two lenses which include outwardly extending filaments which have closed loops on the ends of the filaments. One such lens is known as the "PANNU LENS" and is marketed by American Medical Optics. A second lens having the closed loop at the end of a mounting filament is available from IOLAB under the designation "OSHER LENS." Neither of these lenses includes a centering notch on the filament. There is a Knolle PC-80 lens which has two filaments, one at the top and one at the bottom, with a depression or notch in one side of each filament loop.
Various other devices and techniques have been developed in conjunction with intraocular lenses intended for mounting within the posterior chamber. Lenses including other configurations for the mounting projections of the lens are disclosed in U.S. Pat. Nos. 4,251,887, issued to Anis on Feb. 24, 1981; 4,092,743, issued to Kelman on June 6, 1978; and 3,906,551, issued to Otter on Sept. 23, 1975. A method for implanting an intraocular lens is described in U.S. Pat. No. 4,159,546, issued to Shearing on July 3, 1979.